How Do Fireworks Work?
Fireworks are devices that, when ignited, produce noise, smoke, or displays of light. Fireworks are used for entertainment as well as for military and other purposes. Signal flares are used as distress and warning signals on land and at sea. Star shells, which give a brilliant white light, are used to illuminate battlefields and are sometimes attached to parachutes and dropped from aircraft to illuminate a target for bombing.
Home fireworks were formerly popular for Fourth of July celebrations in the United States. However, for safety reasons, private fireworks displays are now outlawed in most states. Instead, there are now public displays of fireworks, which are held under the supervision of city authorities and of other responsible organizations and agencies.
All fireworks are based on the rapid burning of certain chemical mixtures, such as gunpowder. The oxygen for combustion is obtained from chemicals in the mixture rather than from the outside air. The mixtures used in fireworks are called pyrotechnic mixtures, and the manufacture and use of fireworks is referred to as pyrotechnics. Fireworks are made largely by hand because mechanical methods have not proved entirely successful.
Kinds of Fireworks
There are many different kinds of fireworks, including rockets, wheels, colored lights, Roman candles, and stars.
Rockets usually consist of paper tubes packed with gunpowder. When the mixture burns, it produces a large volume of gas, which is forced out through a small opening at the rear of the tube, propelling the rocket in the opposite direction. Pinwheels, also called Catherine wheels, work on the same principle.
By the addition of certain metal salts to the combustible mixture, fire of different colors may be produced. Strontium nitrate, for example, produces a red color, and barium nitrate gives a green color to the fire. The addition of powdered metals, such as zinc or aluminum, causes a brilliant burst of sparks. For aerial displays, stars made of these mixtures are packed into a paper shell, which is propelled into the air by a rocket. High in the air a gunpowder charge explodes the shell, ignites the stars, and sends them cascading in all directions. Roman candles consist of stars and gunpowder packed in alternating layers in a long paper tube. When burned, the brightly colored stars are shot out at intervals amid a fountain of sparks.
One of the most spectacular applications of fireworks is their use in displays called set pieces. A set piece is a large framework to which fireworks are attached. When ignited, the fireworks form a picture or portrait in colored lights. Thousands of fireworks may be used for the colored lights in a single set piece.
Pyrotechnic mixtures were used for warfare during ancient Greek and Roman times. Greek fire, which is believed to have been invented in the 7th century B.C., was used extensively by the Greeks and Romans in both land and marine warfare. Its composition, kept secret, is not known. However, the Greek fire used for the same purposes in the Middle Ages usually contained pitch, resin, sulfur, and petroleum.
Public displays of fireworks seem to have been introduced in the 17th century, although they were not used extensively until the 18th century. Modern fireworks, with colored-light effects, were introduced early in the 19th century. The first extensive use of fireworks displays for the purpose of entertainment, as opposed to occasions of national celebration, was made at the Crystal Palace, near London, England, in 1865.
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